feat(materials): Фаза 6b — раздатка материала ученикам/классу

- POST /api/materials/:id/share {classId|userId} (teacher/admin): создаёт независимую КОПИЮ
  материала каждому ученику класса (source_title «Раздатка: <учитель>») + уведомление через SSE.
- /my-materials: кнопка «Раздать» на карточках (видна учителю/админу) → выбор класса.
- Хелпер LS.shareMaterial. На этом план «Мои материалы» (6 фаз) завершён.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/controllers/studentMaterialsController.js

@@ -3,6 +3,7 @@
  * A user keeps copies of items saved from live lessons; the copies are
  * independent of the session lifecycle. */
 const db = require('../db/db');
+const { emit } = require('../sse');
 
 const KINDS = ['board', 'note', 'link', 'image'];
 
@@ -129,4 +130,44 @@ function deleteCollection(req, res) {
   res.json({ ok: true });
 }
 
-module.exports = { list, create, update, remove, createCollection, updateCollection, deleteCollection };
+/* POST /api/materials/:id/share — teacher hands a material out to a class or
+   a student. Each recipient gets an independent COPY (survives later edits/
+   deletes by the teacher). Body: { classId } | { userId }. */
+function share(req, res) {
+  const mat = db.prepare('SELECT user_id, kind, title, body, url FROM student_materials WHERE id = ?').get(req.params.id);
+  if (!mat) return res.status(404).json({ error: 'not found' });
+  if (mat.user_id !== req.user.id && req.user.role !== 'admin') return res.status(403).json({ error: 'forbidden' });
+
+  const b = req.body || {};
+  let recipients = [];
+  if (b.classId) {
+    const cls = db.prepare('SELECT id, teacher_id FROM classes WHERE id = ?').get(b.classId);
+    if (!cls) return res.status(404).json({ error: 'class not found' });
+    if (cls.teacher_id !== req.user.id && req.user.role !== 'admin') return res.status(403).json({ error: 'not your class' });
+    recipients = db.prepare('SELECT user_id FROM class_members WHERE class_id = ?').all(b.classId).map(r => r.user_id);
+  } else if (b.userId) {
+    const uid = Number(b.userId);
+    if (Number.isFinite(uid)) recipients = [uid];
+  } else {
+    return res.status(400).json({ error: 'classId or userId required' });
+  }
+
+  const teacherName = (db.prepare('SELECT name FROM users WHERE id = ?').get(req.user.id) || {}).name || 'Учитель';
+  const srcTitle = 'Раздатка: ' + teacherName;
+  const ins = db.prepare(`INSERT INTO student_materials (user_id, kind, title, body, url, source_session_id, source_title) VALUES (?,?,?,?,?,NULL,?)`);
+  let sent = 0;
+  db.transaction(() => {
+    for (const uid of recipients) {
+      if (!uid || uid === req.user.id) continue;
+      ins.run(uid, mat.kind, mat.title, mat.body, mat.url, srcTitle);
+      try {
+        emit(uid, { type: 'notification', notif_type: 'material_shared',
+          message: `Новый материал от ${teacherName}: «${mat.title || 'материал'}»`, link: '/my-materials' });
+      } catch (e) { /* ignore notify failure */ }
+      sent++;
+    }
+  })();
+  res.json({ ok: true, sent });
+}
+
+module.exports = { list, create, update, remove, createCollection, updateCollection, deleteCollection, share };